U.S. Pat. No. 1,937,343 discloses a motor vehicle radiator having tubes of the folded type. The tubes of this prior art document have a seam at an end portion of the cross-section of the tube, the seam being formed by folding the two edge portions of the very thin metal of which the tube is constructed, each upon itself, followed by interlocking the folded portions flat against the inner surfaces of the tube wall.
The transverse curvature of the seam gives a good lock and assists in soldering the seam.
In prior art tubes, a close fit between the inner and outer edge portions of the seam will prevent adequate flux penetration for successful brazing of the inner portion of the seam. This is particularly true for so-called "NOCOLOK" (RTM) brazing. Where the fit is too tight, flux must be drawn in from the outside or from the open ends of the tube. Neither of these brazing methods is reliable.
It is accordingly an object of the present invention to provide an improved structure and an improved method of manufacture.